1. Field of the Invention
Methods consistent with the present invention relate to aligning a non-circular fiber, and more particularly, to aligning a non-circular fiber to match the polarization direction of a component to which the non-circular fiber will be spliced.
2. Description of the Related Art
Optical fibers are formed in many shapes, and include a core surrounded by a cladding to guide the light. A circular fiber has a cladding with a circular cross-sectional shape. A number of non-circular fibers have also been produced, such as hexagonal, octagonal, and rectangular fibers. These fibers have claddings with cross-sectional shapes that are non-circular and do not have rotational symmetry.
One example of a non-circular fiber is D-fiber, which was developed and investigated about a decade ago, and has been gaining wide application in many different areas, such as optical sensing, microcellular mobile communication systems, fiber polarizers, and fiber couplers. As shown in FIG. 1, the cladding (200) of a D-fiber (100) is shaped like the letter “D”. Polarization-maintaining D-fiber may have an elliptical core (300). In recent fiber laser developments, D-fiber has also been used in double cladding fibers as the inner clad to repress the helical mode for higher pump efficiency.
Consistent and time-efficient D-fiber splicing is required for the production lines of components such as fiber gyroscopes and fiber amplifiers. Two primary challenges in low loss fusion splicing of D-fiber are polarization alignment and fiber core alignment. Many methods and approaches have been developed and tested for splicing different polarization fiber types and rare earth doped active fibers. However, only a very limited number of publications discuss D-shape fiber splicing.
For example, the article “Low loss elliptical core D-fiber to PANDA fiber fusion splicing,” 1 Sep. 2008/Vol. 16, No. 18/OPTICS EXPRESS 13559 by Joshua M. Kvavle, Stephen M. Schultz, and Richard H. Selfridge describes a method in which D-fiber is spliced to PANDA fiber using an elliptical-core fiber in a bridge splice. First the PANDA fiber is spliced to the elliptical-core fiber, and then the elliptical-core fiber is spliced to the D-fiber. Elliptical-core fiber is chosen as the bridge fiber because its circular cladding matches the circular cladding of the PANDA fiber, and its elliptical core matches the elliptical core of the D-fiber. The core of the elliptical-core fiber is expanded to match the mode of the PANDA fiber, and the D-fiber is connected to the elliptical-core fiber using a low temperature splice. This method requires the polarization alignment to be performed manually, resulting in time-consuming extinction ratio measurements. Although this process can be performed in a laboratory setting, it is too costly in both equipment and labor time to be used in production.
Further, as shown in FIG. 3A, a length of D-fiber (100) may be slightly bowed or curled when suspended from one end. This effect is caused by the mismatch in thermal expansion between the silica body and the doped guiding region. This characteristic of D-fiber presents challenges in cleave quality, splicer rotational alignment, and splice loss.